1. Field of the Invention
This invention relates to a water-cooled thrust combustion grate for refuse combustion plants that is particularly well suited for the combustion of refuse and waste with high heating values. Such thrust combustion grates have stationary and movable grate levels comprising grate plates or a row of grate bars, with the grate plates resting on top of each other in a stair-like manner. These thrust combustion grates can be assembled so that the combustion bed is essentially horizontal, or possibly inclined, with slopes of up to 20 degrees or more being usual. The grate plates are preferably made from sheet steel and form panel-shaped hollow elements which extend across the entire width of a grateway, through which water is fed as a cooling medium. Every second grate plate is movable, allowing it to perform a stoking or transporting stroke. In the case of a forward feed grate, the leading edge of the movable grate plates pushes material to be combusted forward onto the next grate plate down. In contrast thereto, a reverse feed grate forms a back to front built-in sloped stairway, so to speak. In a reverse feed grate, the leading edges of the movable grate plates transport the material behind them backwards which then rolls back down the slope of the grate. The movable grate plates, i.e. the grate plates in-between two stationary grate plates, are usually moved collectively to and fro in the downward direction of their inclination. This ensures that burning refuse lying on the grate for high dwell times of 45 to 120 minutes is constantly turned over and distributed evenly over the grate.
2. Description of Prior Art
European patent document EP-0'621'449 discloses a water-cooled thrust combustion grate. This grate has grate plates which extend over the entire width of the grateway, that is, which do not comprise a plurality of grate bars per grate level. The movable grate plates, like the stationary ones, are suspended by their back edge on crossbars which, when operated, move collectively forwards and backwards, thereby displacing the movable grate plates. One of the disadvantages of this means of driving the movable grate plates is that any small item that becomes jammed at the side between the grate plate and the outer side panel can cause the grate plate to skew to the side; that is, as seen from the top, the plate no longer lies exactly parallel to the adjoining stationary grate plates. If it is then displaced while in this position, high leverage forces occur, as a result of which the plate comes into contact with the outer side panels. The drive forces then required are correspondingly high. The wear caused by the enormous friction force is considerable and reduces the service life of the entire grate. Furthermore, the drive means is designed in such a way that an individual drive for each movable grate plate, which would be desirable to optimize the combustion process, could only be installed at phenomenal cost.
International Patent Application PCT/IB94/004113 discloses a thrust grate module featuring individual drives for the movable grate plates. Here, the movable grate plates roll on steel rollers, but are only guided with respect to the outer side panels by means of sliding friction. The drive is effected by hydraulic piston-cylinder units which come into contact with the approximate center of the grate plates. Even with this construction, skewing to the side is impossible to avoid. If a small particle gets jammed between the grate plate and an outer side panel, very high friction forces occur which, firstly, require correspondingly large hydraulic cylinders to overcome them and, secondly, cause correspondingly high wear.